Quick Answer
Cv and Kv both measure valve flow capacity — how much fluid passes through at a given pressure drop. Kv = 0.865 × Cv (exact IEC 60534 factor). Use Cv for US/ANSI projects; use Kv for European/IEC projects. The conversion is linear and applies to any valve type.
- Cv → Kv: multiply by 0.865 (e.g. Cv 100 = Kv 86.5)
- Kv → Cv: multiply by 1.156 (e.g. Kv 100 = Cv 115.6)
- Cv defined: US gpm of 60 °F water at 1 psi pressure drop
- Kv defined: m³/h of 15 °C water at 1 bar pressure drop
Convert a valve Cv (US) to Kv (metric) and back, using the exact IEC factor. Kv = 0.865 × Cv.
Conversion
Cv is gpm of water at 1 psi; Kv is m³/h of water at 1 bar.
Quick reference
| Cv | Kv |
|---|---|
| 1 | 0.865 |
| 10 | 8.65 |
| 50 | 43.3 |
| 100 | 86.5 |
Frequently Asked Questions
How do I convert Cv to Kv?
Multiply Cv by 0.865. For example, Cv 50 = Kv 43.3.
How do I convert Kv to Cv?
Multiply Kv by 1.156.
Why 0.865?
It comes from the unit difference: gpm at 1 psi versus m³/h at 1 bar.
Are Cv and Kv the same thing?
They measure the same flow capacity in different unit systems.
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Related Resources
What Are Cv and Kv — and Why Do They Matter?
The valve flow coefficient is the single most important number in valve sizing. It tells a process engineer how much a valve restricts flow: a higher Cv (or Kv) means less restriction. Every valve selection — from a ½″ ball valve on a laboratory bench to a 24″ control valve on a crude oil header — starts with calculating the required Cv and then choosing a valve whose rated Cv comfortably exceeds it.
Cv is the US customary unit, defined by the Instrument Society of America (ISA S75.01 / ANSI/ISA-75.01.01): it equals the flow in US gallons per minute (gpm) of 60 °F water that will pass through the valve with a 1 psi pressure drop. Kv is the metric equivalent defined by IEC 60534-2-1: m³/h of 15 °C water at a 1 bar differential. The two coefficients measure exactly the same physical property — they differ only in units.
When to Use Cv vs Kv
| Situation | Use | Reason |
|---|---|---|
| ANSI / ASME pipeline projects (North America) | Cv | ISA, API, and most US valve datasheets quote Cv |
| IEC / EN pipeline projects (Europe, China, international) | Kv | IEC 60534 and most European valve catalogs use Kv |
| Control valve selection (Fisher, Emerson, Flowserve) | Cv | US manufacturers publish Cv in product data |
| DIN / PN-rated valve selection (Samson, Bürkert, Siemens) | Kv | European manufacturers publish Kv |
| PLC / DCS engineering with mixed vendor quotes | Convert to one system | Use this tool to normalize before comparison |
Worked Conversion Examples
Example 1 — Cv to Kv (selecting a European valve for a US-specified system)
Your process engineer specifies a required Cv of 75 for a liquid isolation service. The European valve supplier quotes products in Kv. Convert: Kv = 0.865 × 75 = 64.9. You need a valve with rated Kv ≥ 64.9 — the supplier's DN80 ball valve rated at Kv 80 is a suitable choice.
Example 2 — Kv to Cv (sizing from a European datasheet for a US project)
A German-sourced butterfly valve is rated Kv 1,200. Your ANSI piping spec requires Cv. Convert: Cv = 1.156 × 1,200 = 1,387. Compare this to the required Cv you calculated from flow and ΔP to confirm the valve is adequately sized.
Extended FAQ
Does the Cv / Kv conversion factor change for different fluids?
No. The 0.865 factor is purely a units conversion — it converts the pressure-drop and flow-rate units, not the fluid properties. For fluids other than water, you must apply a separate fluid correction factor (Fp for piping geometry, FR for Reynolds number, FF for critical pressure ratio) when calculating the required Cv, but the Cv ↔ Kv conversion itself is always 0.865.
Can I use this converter for gases and steam?
Yes — a valve's Cv rating is inherently a water-based coefficient, but the conversion between Cv and Kv is unit-only and applies equally to valves used for gas or steam service. Use our Valve Cv Calculator to first compute the required Cv for gas or steam, then convert to Kv here if needed.
What is the difference between rated Cv and required Cv?
Required Cv is calculated from your actual flow and pressure drop. Rated Cv is the manufacturer's published maximum flow coefficient for the valve at full open. You must select a valve whose rated Cv exceeds your required Cv, typically by 20–30% margin, to avoid operating the valve at near-full-open — which reduces controllability and accelerates wear.
Where can I find the rated Cv for a specific ball valve size?
Our Ball Valve Sizing Calculator includes a reference table of typical full-bore ball valve Cv by size (½″ through 12″). For specific products, consult the manufacturer's ISA sizing data sheet or IEC 60534 test report.